Preparation of a printing surface



Dec. 5, 1950 c, w, `BENNETT Er AL 2,532,390

PREPARATION 0F A PRINTING SURFACE Filed Hay 28, 1945 Jup/aart :Sgo/uhm of wrgy/ res/n ala/aim' bau/'face avc/maffe.

C Wenpef WEA lex ander j Invenzozs n l Aorney Patented Dec. '15; '1l-95.0

PREPARATIONOF A PRINTING SURFACE Charles W.` Bennett, Rochester, N. Y., and

William F. Alexander, Cleveland, Ohio, assignors to Rochester Institute of Technology, Rochester, N. Y., a. corporation of New Yorlr Application May 28, 1945, Serial No. 596,410

(Cl. 4l-25) 1 Claim.

This invention relates primarily or broadly to the preparation of a printing surface, having for its object to provide a process therefor which is simple in execution, cheap in cost, and productive of better results than similar processes heretofore proposed.

This disclosure more specifically pertains to the conditioning of a body or bodies of the nature of gelatine, for instance. The bodies may be on a support as a continuous covering, from which selected portions may be removed, leaving the above mentioned bodies or parts which are desired to be conditioned. The delineation of the parts to condition, on the other hand, may be made on a continuous covering of material on a base which may be separated therefrom, after transferral of the delineated covering to a new support. Lastly, the bodies to be conditioned may be put on a support by spraying or brushing as through a stencil of predetermined form.

Hereinafter the body to be conditioned will be referred to as a gelatine image, whether obtained manually or photographically, and may comprise gelatine alone or gelatine partially hardened to render it insoluble in Water for purposes of separation of selected areas from a continuous nlm or covering.

A delineation of areas may be made by exposure in a camera oi a picture or any color relief, direct or through a light intercepting screen, onto a gelatine-silver halide film, which may be on a removable paper support, for instance. if this is developed in a tanning developer and squeegeed face down to another support, as for instance a metal plate, a treatment with warm water will permit the removal of the original support for the gelatine-silver halide nlm, as Well as the removal of the portions of this nlm which were unacted upon by light. Therefore, there is obtained on the new support a delineation, predetermined by the color relief copy and flexible as to size, represented by a partially hardened gelatine. The partially hardened gelatine covers or represents the parts corresponding to the whites of a black and White color relief, While the parts which were removed from the new support correspond to the blacks of said color relief.

In some cases it is necessary to have a reversal of the above condition. This is accomplished by preparing in the camera, correct as to size, a negative as made above, except that ordinary film is used upon which the delineation is made. Using this negative, a print may be made on the film with separable support mentioned above, developed in tanning developer and transferred to another support, treated as above, whereupon the delineation is a positive instead of a negative as first given. It is obvious that with contact printing, for instance, producing the positive delineation, the gelatine film may be of the dichromated type and the support before printing may be the Iinal one. In other words, the delineation may be made in situ, rather than being transferred.

This delineation, however obtained, is a body of gelatine in more or less plastic form. For some purposes, it is desirable to harden the mass so that rather heavy pressures may be applied without distortion as in the case of making newspaper mats Where pressures of the order of 4,000 pounds per square inch may be employed. When the gelatine image is used in the direct transfer of inl: to paper, for instance, a hardness and toughness capable of repeated transfers is desired in said gelatine image.

Several agents have been discovered for hardenlng, so that the degree of hardness desired in said gelatine image will determine the proper agent or agents to use. Also, depending on what is desired, it is possible to harden the gelatine in the dried condition more or less throughout the mass, or it is possible to harden the air exposed surface of the image, leaving the bulk of the material in the moist condition, thereby enabling the image to withstand considerably more pressure (without distortion) than an image not so treated. The image may be hardened while wet, or it may be dried iirst; or it may be surface hardened only, leaving the inner parts moist.

Types of hardening agents used, and typical solutions thereof, are as follows:

l. Formaldehyde and vegetable tanning agents.

2-3 oz. of tannic acid dissolved to make one gallon with 40% formaldehyde solution, i. e. the ordinary commercial formaldehyde. There may be added 12-18 ozs. of glycerine to this, as a conditioner for the gelatine.

Acid chrome tanning. A water solution of chromic acid, which is generally made by dissolving say 15 ounces of potassium dichromate and eight ounces of commercial muriatic acid to make 1 gallon. The reducing solution may be 10-20 ounces of "hypo per gallon, made acid with acetic acid.

` 3. Basic chrome tanning. Dissolve in hot water sodium aluminate. (a) Sodium silicate solution may be the commercial grade, sold for preserving eggs, diluted with 1 volume of water. (b) Sodium tungstate 10-15 ounces per gallon of water.

5, Thermo-setting resins such as phenol formaldehyde condensation product. Alcohol solution of the product formed by the condensation of phenol and formaldehyde. Ordinary commercial impregnating solutions are available. Concentration may be changed by dilution with alcohol.

6. Thermoplastic agents such as cellulose nitrate or acetate, methyl methacrylate and vinyl acetate or vinyl chloride or their co-polymers. 10-15 ounces of Vinylite per gallon of ethylene dichloride, or 8-15 ounces of Vinylite per gallon of methyl ethyl ketone.

Type 5 is used in solvents for the unhardened resin, while type 6 may be used in solvents from which a satisfactory film is obtained, since the excess or part not entering the gelatine will remain as a continuous film over the entire surface. The amount of impregnation of the gelatine image may be controlled somewhat by a choice of solvents for the plastics. For example, solvents not miscible with water will not impregnate a moist gelatine image with plastic as thoroughly as if the solvent for the plastic were miscible with water. It is apparent therefore that varying degrees or impregnation can be obtained from a maximum to a surface effect by selection of the solvent. For example with vinyl co-polymer, ketones are water imiscible solvents, while chlorinated hydrocarbons are very slightly water soluble or immiscible.

rI'ype 2 gives a more thorough impregnation than type 3, acid and chrome tannage, being a two-solution treatment, allows first a thorough impregnation with chromic acid, and then a deposition of the tanning material by treatment subsequently with hypo solution. On the other hand with the basic method, the tanning material being furnished directly from the one solution, gives greater hardening action towards the surface of the image.

In operation one procedure may be as follows: The copy for reproduction is placed on the camera copyholder and an exposure made for the production of a negative either on ordinary lm or on a lm with a removable support.

In the latter case, the film is developed in a tanning developer, treated to stop the full development, partially dried as by soaking in alcohol, and then squeegeed face down on a dimentionally stable support such as a metal plate. The assembly is then placed in warm water containing agents which retard swelling of the gelatine, and prevent further photographic development. The original lm support is removed and the unexposed parts, i. e. the parts not tanned by the developer, removed by agitation of the warm water solution, down to the surface of the dimensionally stable support above mentioned.

The remaining part or that representing the negative image of the copy, is placed in a saturated sodium chloride solution, to remove excess Water from the gelatine. It is then placed for two minutes in a 40% formaldehyde solution containing 2-3 ounces of tannic acid, and 12-18 ounces of glycerine, per gallon. After rinsing it is returned to the saturated salt solution to remove excess water, and then subjected to a 1/2 minute treatment in a water solution containing 2 ounces of ammonium dichromate per gallon.

Then it is rinsed well with water, and the excess water blotted out with newsprint paper, after which compressed air is utilized to blow out all parts until the coverage laterally is as desired for the Work at hand.

At this point the whole image is covered, by flowing or brushing, with a solution of thermoplastic or thermosetting resin the solvent of which should not be readily miscible with water, since a minimum of penetration of the gelatine is desired so as lnot to disturb the image structure at this point. The material used may be determined by the character of the embossing to be made from this negative image; that is to say, if the embossing is to be made in thermoplastic resin, this should be used as the material for coating the negative. This coating amalgamates with and becomes a part of the embossed plate (below). A typical coating solution is: 1 ounce of Vinylite dissolved in 10 ounces of ethylene dichloride. The solvent is evaporated by blowing with heated air, and within a reasonable length of time (up to 1 hr.) a positive reproduction is obtained from the treated negative plate, by the application of iiuid or plastic material to said plate, forming a relief printing surface from the bare portions of said plate. rfhe term Vinylite as used herein, is the trademark for a product produced by combining the well known esters of vinyl acetate and vinyl chloride; the treatment polymerizing these materials, and when they are together they are called co-polymers.

The development made here is in the direction of "case hardening the surface of the negative parts, accomplishing two objects, namely, to enable these parts to withstand greater pressure without distortion, and advantageously accomplishing the enclosure or entrapment of moisture and other agents within the body of the gelatine while the surface is dry and hard. These entrapped agents are relief producing agents and are more especially moisture or water, glycerine or any agent dissolved in the water which might render the complex, i. e. the moist gelatine, stable. For the purposes of this patent application, these agents have been covered in the former patents and are merely explanatory; that is to say these agents may be of various compositions, nature and resultant effect, all as clearly disclosed in and covered by U. S. Letters Patent No. 1952787 granted March 27, 1934 entitled Method of Printing, and No. 1990925 granted Feb. 12, 1935 entitled Method of Preparing a Plate for Printing Purposes, each granted to Charles W. Bennett (one of present applicants). The positive reproduction is obtained from this treated negative plate by the application of fluid or plastic materials to said plate, forming a relief printing surface from the bare portions of said negative plate.

In the former case where the negative is made on ordinary photographic film, it is developed and a positive printed on a sensitized lm on a removable support. In the latter case the lm must be transferred to a dimensionally stable support as before mentioned. If the sensitized iilm is of the dichromated type, development and removal of unexposed parts is by water, while With the gelatine-silver halide type, the photographic development is in a tanning developer, and the removal of the unexposed parts is by water as above.

In order to better understand the procedure, follow the case of the gelatine-silver halide emulsion on a removable support. Reference is made to the llow diagram illustrated on the accomthe step of chrome panying drawing wherein the principal sequential steps of the procedure are briefed. The contact print from the film negative is developedV y acid solution (#2 above) followed by a like time in the reducing or minutes treatment tion (#3 above), it may be treated hypo solution above, or l-2 in the basic chrome alum soluand after rinsing with water with a solution of commercial sodium silicate or water glass diluted with one to two volumes of water. After thorough rinsing in running water. the plate is dried, preferably by whirling first and finally by blowing with hot air, whereupon it is ready for printing. 'Ihis treatment is sufficient for the preparation of a printing plate for direct printing where the number of impressions is not too great.

However, where extreme toughness and hardness is required, such as the use in making newspaper mats, an alternative treatment is advantageous. This consists of impregnating the gelatine relief with a solution of plastic materials. The latter may be thermoplastic of thermosetting depending upon the requirements of the plate. For instance if the mat is to be made under heat, the material must be thermosetting. The thermosetting plastics impart a more permanent character to the plate. This treatment may follow hardening by types 2 or i3, or the impregnation of the gelatine may be accomplished immediately after the step of washing out the unexposed and unhardened (by tanning developer) parts, these 'steps being those set forth in the preceding paragraph. In either case the plate is thoroughly dried as above stated by whirling and/or blowing with hot air, and the solution of the plastic applied uniformly over the face of the plate. either by brushing, flowing or dipping. The solution may be an alcohol solution of unhardened phenol formaldehyde resin for a thermosetting plastic. or a solution of "Vinylite dissolved in methyl-ethyl-ketone (or its homologues) fora thermoplastic material. These are water miscible solvents and tend to impregnate the gelatine. After standing for 1-2 minutes, the solvent is removed by evaporation whereupon, with the thermoplastic impregnation, the plate is ready for printing purposes. With the thermosettlng plastic the plate must be heated 3-5 minutes at 300 F. or above, to set the plastic, whereupon the relief becomes capable of imparting its full depth to a mat with or without heat, or may be used for direct printing.

The support for these positive surfaces may be metal. or a composite of the nature of hard cel- 'lulosic material, the requirements necessarily comprising a. goodsuriace and sumclent stability to accomplish the particular purpose.

Individual negatives may be massed in fiat form and printed on the sensitized material for a positive flat. After the hardening treatment, the flat is cut into individual parts and if the material is of a nature to require it, the edges of the cuts may be covered with plastic, for instance, to prevent the introduction of moisture with a consequent separation of the positive parts from the support.

It is obvious that those skilled in the art may vary the steps and combinations of steps constituting the process of this invention without departing from the spirit thereof, and therefore it is `desired not to be limited to the exact foregoing disclosure except as may be required by the claim.

What is claimed is:

The process of producing a printing surface which comprises forming photographically in a camera a reproduction of an object on a silverhalide sensitized gelatine film, treating the film with a tanning developer, partially drying the developed lm, and swqueegeeing the film face downon a stable support; removing the unexposed parts of the film by washing in a warm water solution containing agents which retard swelling of the gelatine and which prevent further photographic development, thereby establishing covered and bare portions of the stable support, the covered portions comprising an image of the object, said image being moist and having a certain relief with regard to the surface of the stable support; subjecting the moist gelatine image thus established to a saturated sodium chloride solution to remove excess water from the gelatine; treating the moist gelatine image substantially for 2 minutes in a 40% formaldehyde solution containing 2 to i3 ounces oi' tannic acid and approximately 12 to 18 ounces of glycerine per gallon to partially harden the image; rinsing and removing excess water by treating with the saturated salt solution; sub- V-jecting for approximately 1/2 minute :the moistv partially hardened gelatine image to a water solution containing approximately 2` ounces of ammornium dichromate per gallon; rinsing well with water, and removing the excess water to leave the gelatine image relief in a moist condition;

I applying a solution of vinyl resin to the surface area. of the image; removing the excess of said resin, heating, and drying; and utilizing the dried image surface for printing purposes.

CHARLES W. BENNETT. WILLIAM F. ALEXANDER.

, REFERENCES CITED AThe following references are of record in the ille of this patent:

UNITED STATES PATENTS 

